In wireless communication systems, wireless service providers may operate radio access networks (RANs), each RAN including a number of base stations radiating to provide coverage in which to serve user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the RAN may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Further, a RAN may operate in accordance with a particular air interface protocol, examples of which include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) and Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1xRTT and 1xEV-DO), Global System for Mobile Communications (GSM), IEEE 802.11 (WIFI), BLUETOOTH, and others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between base station coverage areas, and other functions.
In accordance with the air interface protocol, each base station may provide wireless service to UEs on one or more carrier frequencies (carriers), each of which could be frequency division duplex (FDD), defining separate frequency channels for downlink and uplink communication, or time division duplex (TDD), defining a frequency channel multiplexed over time between downlink and uplink use. Each carrier or its respective channels could be within a defined frequency band and could be of a particular frequency bandwidth, such as 5 MHz, 10 MHz, or 20 MHz for instance, defining a certain extent of air interface resources. A given base station could be arranged to serve a UE on a single such carrier at a time or, with carrier aggregation service or the like, on multiple such carriers at a time.
Further, each base station in such a RAN may be communicatively linked with a signaling controller that carries out various network control functions, such as managing setup of bearer connections between the base station and one or more transport networks, tracking where UEs are located in the RAN, paging UEs, and the like. In addition, neighboring base stations may be communicatively linked with each other, to facilitate handover and other inter-base station signaling.
By way of example, in an LTE RAN, each base station (LTE evolved Node-B (eNodeB)) has a communication interface with a signaling controller known as a mobility management entity (MME), the base station and MME each also have a respective communication interface with a gateway system that provides connectivity with a packet-switched transport network, and the base station has a communication interface with each of its neighboring base stations. Typically, the nodes of such an LTE RAN would sit on a wireless service provider's core packet-switched network (e.g., a network compliant with the industry standard system architecture evolution (SAE) for the LTE protocol), and so the base station and each other RAN entity (e.g., MME, gateway, and neighboring base station) may each have an assigned Internet Protocol (IP) address on that network, and the interfaces between these entities may be defined as logical connections (e.g., established virtual tunnels) through that network.
In example operation, when a UE enters into coverage of an LTE base station on a particular carrier, the UE signals to the base station to initiate an attach process and to establish a radio-link-layer connection with the base station. In this process, the base station signals to the MME, the MME authenticates the UE, the MME and base station obtain and store a context/profile record for the UE, and the gateway system assigns an IP address to the UE for use by the UE to communicate on the packet-switched transport network. Further, at this point or later, the MME may engage in signaling with the base station and the gateway system to establish for the UE one or more bearers for carrying packet data between the UE and the transport network.
Once a UE is so attached with a base station, the base station then serves the UE on one or more carriers, managing downlink communication of packet data to the UE and uplink communication of packet data from the UE. For example, as the gateway system receives packet data destined to the UE, the gateway system may forward the packet data to the base station, and the base station may schedule and provide transmission of that data to the UE on the UE's serving carrier(s). Likewise, as the UE has packet data to transmit on the transport network, the UE may transmit a scheduling request to the base station, the base station may schedule transmission of that data from the UE on the UE's serving carrier(s), the UE may accordingly transmit the data to the base station, and the base station may then forward the data to the gateway system for output on the transport network.
In order to utilize legacy cellular networks, a service provider may implement a hybrid wireless communication system that includes multiple separate but interconnected RANs. For example, a service provider may implement a first RAN that provides high speed data communications, and a second RAN that provides traditional telephony service, with each RAN providing air interface coverage according to a different air interface protocol. In such an arrangement, a UE may acquire connectivity with and be served by the first RAN and may at some point transition to instead connect with and be served by the second RAN. For instance, some existing hybrid systems include an LTE RAN (e.g., the LTE RAN discussed above) for data communications and a circuit-switched RAN, such as a CDMA RAN (or GSM RAN or the like), for legacy telephone service.
A UE that operates in a hybrid system may be configured as a single radio device, which utilizes the same radio system for communications on both networks in the hybrid system. In the context of a hybrid system utilizing LTE for data communications, a UE with the capability of using one radio system for both LTE communication and communication under at least one other protocol (e.g., CDMA) may be referred to as a single-radio LTE (SRLTE) device or an SRLTE UE. Similarly, when using a single radio system to engage in communication under LTE and at least one other protocol may be referred to as operating in an SRLTE mode.
When operating in a hybrid system, an SRLTE UE can register with both the LTE network and the CDMA network. However, when LTE service is available, an SRLTE UE will remain connected to the LTE network, except for cases when communication via the CDMA network is needed, such as tuning away to listen for pages or initiate a voice call via the CDMA network. As such, an SRLTE UE periodically disconnects from the LTE network and tunes to the CDMA network (e.g., at scheduled paging occasions) to check for any page messages directed to the UE from the CDMA network. If the SRLTE UE does not receive a page from the CDMA network, then UE, it will re-connect to the LTE network.